Capacitive and inductive load impedances on output drivers of conventional memory cards result in weak output eye performance at high frequencies. Distortion caused by pins, connectors and traces from the memory card across a data bus to other circuitry limits an upper frequency for reliable data transmission. Degradation of the output eye results in poorer receiver margin tests. In conventional driver designs, for a multi-drop double-data rate fourth generation (DDR4) memory channel where an off-target termination is VDD referenced, having a symmetric pullup/pulldown Ron driver would introduce significantly more reflection due to extra drive strength already present on the line from off target terminations.
It would be desirable to implement an asymmetric on-state resistance driver optimized for multi-drop DDR4.